In regulator circuits particularly, there have been many different systems devised for sensing the output current of a regulator having a DC output. U.S. Pat. No. 3,388,309, for example, shows a voltage regulator which has electrical conductivity isolation between the input and the output. U.S. Pat. No. 3,859,586 discloses a variable response peak detector circuit and U.S. Pat. No. 3,916,282 discloses a peak current detector. U.S. Pat. No. 3,764,881 is directed to a DC-to-DC converter which regulates the output voltage. An FET transistor is used to sample the voltage across the transformer primary winding and the transistor is gated on at a time just prior to the time that the transformer field collapses.
In many regulator applications (for example, a switching regulator is a type currently in favor), the regulator operates from commercial frequency and voltage conductors, for example, 230 volts and 60 Hertz, and it is desired to supply a low voltage/high current DC output. This might be used to power a computer or a computer terminal and the voltage output might be a low 5 to 15 volts DC, with the current at a high level, say 100 to 300 amperes. This makes large diameter conductors in the DC output circuit to carry this large amperage, and, in one prior circuit, a current transformer was connected in the low voltage AC output to the final DC rectifier; however, this required the current transformer to have a core sufficiently large to pass the single turn of the output lead through the center of this core. Even with a large transformer turns ratio reduction in the current from the current transformer, large sizes of diodes were required in the output circuit from this current transformer secondary. With circuits having high output currents, several problems arose, including the requirements for two costly current transformers with a large number of secondary turns, and, additionally, it became very difficult to pass the primary turn through the transformer core because of the large conductor size. Also in very large current units, multiple parallel diodes are required to carry the current, and in such case multiple current transformers must be used.
Another problem in the prior art circuit was to provide some means for detecting the peak current carried by the power semiconductors, either transistors or thyristors, so it had been previously known to utilize a current transformer and a diode bridge, with the primary winding of the current transformer connected in the primary winding circuit of the inverter to generate a peak current signal.